Module documentation for 0.2.15

This library is based on an STM-specialized implementation of
Hash Array Mapped Trie.
It provides efficient implementations of Map, Set
and other data structures,
which starting from version 1 perform even better than their counterparts from "unordered-containers",
but also scale well on concurrent access patterns.

For details on performance of the library, which are a bit outdated, see
this blog post.